reliability: added unittests for SimpleResultSetItem
reliability: added unittests for SimpleResultSet construction
Merge branch 'develop' into feature/unittests1.1

Merge in cheshire3.resultSet bug fixes
reliability: added unittests for combining SimpleResultSets
reliability: added tests for ResultSet relevance scores
reliability: added tests for combining ResultSet relevance scores
style: renamed classes used in tests to avoid confusion

e.g. 'TestDatabase' might lead a reader to infer incorrectly that a
Database is being tested. Rather a Database is faked to enable
ResultSets to be tested. TestDatabase -> FakeDatabase etc.
reliability: added unittests for simple file-based Logger
Merge branch 'develop' into feature/unittests1.1
tests: added tests for ResultSet serialization
bugfix: SimpleResultSet serialization bug fixed

Fixed bug when serializing SimpleResultSet attributes with None values.
tests: added unittests for ResultSetStores
bugfix: missing expiresReverse file for BdbResultSetStore
tests: fixed bugs in cheshire3.tests.testResultSetStore

- Return value for create_resultSet is an identifier, not the ResultSet

- ResultSet _should_ be altered by storing - gains ``id`` attribute
  test modified accordingly
bugfix: ResultSet class serialization by SimpleResultSetStore

fixes #55
tests: use shutil.rmtree in tearDown for testBaseStore

Attempting to to resolve issue #54
docs, tests: fixed typo in docs for cheshire3.utils.dotProduct

Docs for this function include examples that can be run as unittests
using the doctest module
tests: added unittests for cheshire3.utils.SimpleBitfield

Hopefully will assist investigations into issue #42
tests: fixed typo in unittests for ResultSetStores
tests: added basic unittests for Indexes